Drilling fluid dispersant

ABSTRACT

An aqueous drilling fluid having present in an amount sufficient to disperse the fluid and to provide resistance to high temperatures and solids contamination of the drilling fluid, at least one salt of a polymer or copolymer of acrylic or methacrylic acid with alkanolamine, alkylamine, mixtures of alkanolamine and alkylamine, mixtures of lithium and alkanolamine, mixtures of lithium and alkylamine and mixtures of lithium, alkanolamine and alkylamine, the polymer having a weight average molecular weight of between about 2,000 and about 15,000 and a pH of from about 6 to about 8.5 and where mixtures of lithium and alkanolamine, lithium and alkylamine or mixtures of lithium, alkanolamine and alkylamine are used, the amount of lithium is present to give from about 30% to about 70% of the desired neutralization of the polymer and the alkanolamine and/or alkylamine is present to give from about 70% to about 30% of the desired neutralization of the polymer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a drilling fluid dispersant having improved temperature stability, dispersing properties and "solids contamination" tolerance.

2. Description of the Prior Art

U.S. Pat. No. 2,552,775--Fischer et al, issued May 15, 1951, describes a water based clay drilling fluid containing an alkali metal or ammonium polyacrylate salt having a molecular weight greater than 2,000 as a protective agent for controlling filtration rates, viscosities and other properties as well as preserving and/or increasing producing formation permeabilities.

U.S. Pat. No. 2,603,598--Meadors, issued July 15, 1952, describes a water based clay drilling fluid containing sufficient alkanolamine to increase pH to at least 10 without unduly increasing viscosity.

U.S. Pat. No. 2,718,497--Oldham et al, issued Sept. 20, 1955, describes a water based clay drilling fluid containing a linear hydrocarbon chain polymer acid salt such as a polyacrylic acid salt having a molecular weight greater than 10,000 to control water loss. The salt is produced by reacting alkali metal hydroxide, ammonium hydroxide or an alkanolamine with the acid.

U.S. Pat. No. 4,370,171--Robinson et al, issued Jan. 25, 1983, describes a method for dispersing a comminuted solid in aqueous medium using a salt of alkanolamine and polymeric carboxylic acid. Polymeric carboxylic acids such as polyacrylic acids may be used.

U. D. Mamadzhanov et al in Tr. VNII Ekon., Organiz. Proiz-Va I Tekhn.-Ekon. Inform. V Gaz. Prom-Sti (1974) 114-117 describe synthesis of chemical reagents based on acrylic polymers and aminoalcohols. A study of these reagents on clayey solutions has shown that they may find practical application in deep well drilling.

Japanese Patent Public Disclosure No. 60-133085-Nippon Oils and Fats KK published July 16, 1985 describes a mud additive to improve heat, salt and cement resistance of a water based clay drilling fluid. The additive may be (a) polyacrylic acid having a 1000-20,000 molecular weight or (b) an alkali metal, ammonium or alkanolamine salt of (a) having a degree of neutralization of 30% or less.

SUMMARY OF THE INVENTION

High temperature stability, dispersing properties and tolerance to "solids contamination" of a water based clay drilling fluid are improved by addition of sufficient low molecular weight salts of polyacrylic acid, polymethacrylic acid or copolymers thereof with alkanolamine, alkylamine, mixtures of alkanolamine and alkylamine and with mixtures of lithium and alkanolamine, mixture of lithium and alkylamine and mixtures of lithium, alkanolamine and alkylamine having a pH from about 6.0 to about 8.5 as a dispersant. The pH is indicative of the degree of neutralization of the polymer. Copolymers containing at least 50% acrylic acid or methacrylic acid may also be used. Molecular weight of the polyacrylic acid, polymethacrylic acid or copolymer acid may be from about 2000 to about 15,000. From about 0.1 to about 5.0 ppb (pounds per barrel) of one of the above salts may be added to the drilling fluid.

DETAILED DESCRIPTION

In drilling an oil, gas, thermal or water well with rotary drilling tools, hollow drill pipe with a rotary bit attached to the lower end is used. The drill pipe with attached bit is rotated in the borehole. A drilling mud or fluid is pumped down the hollow drill pipe and through the bit at the bottom of the borehole and then up to the surface through the annular space between the drill pipe and the borehole wall. The drilling fluid is a suspension of solid material in a liquid medium such as water. It may contain other additives. The drilling fluid lubricates and cools the drill bit, suspends and carries cuttings out of the borehole, coats the wall of the hole with a thin impervious layer of solid material to prevent flow of fluids into or out of the formation and exerts a hydrostatic pressure to the formation to counterbalance the pressure of liquids or gases present therein.

For a drilling fluid to perform its functions, it must have certain desirable physical properties. The fluid must have a viscosity that is readily pumpable without undue pressure differentials. It must be sufficiently thixotropic to suspend the cuttings in the borehole when fluid circulation stops. The fluid must release cuttings from the suspension when agitating in the settling pits. It must form a thin impervious filter cake on the borehole wall to prevent loss of liquid from the drilling fluid by filtration into the formations. Such a filter cake effectively seals the borehole wall to inhibit any tendencies of sloughing, heaving or cave-in of rock into the borehole. Further, the fluid must be capable of suspending high specific gravity weighting agents such as inorganic heavy metal compounds to maintain a pressure substantially greater than the hydrostatic pressure of a column of water of equal depth against a formation when necessary. The composition of the fluid should also be such that cuttings formed during drilling the borehole and can be assimilated or dissolved in the fluid without affecting physical properties of the drilling fluid.

An other important characteristic of a drilling mud is that their viscosities should be such that they are readily and easily circulated by pumping at those pressures ordinarily employed in drilling operations.

Previous drilling fluids include clay slurries such as water-based bentonite clay slurries which are used as drilling fluids. To disperse the solid materials in these fluids, a dispersant such as ferrochrome lignosulfonate (FCLS) is required. However, when FCLS containing slurries are used at extremely high temperatures, FCLS breaks down the drilling fluid gels.

Another dispersant system, which is also used with drilling fluids, is a combination of FCLS and a sulfonated polystyrene maleic anhydride copolymer. This system requires two components, maintenance of the FCLS, and is more expensive.

Still another dispersant system, which is used with drilling fluids is polyacrylic acids having molecular weights less than 8,000. These dispersants are very effective at low concentrations but are sensitive to drilled solid contamination which renders them less effective at high temperatures and reduces their dispersing properties.

The present invention provides water based drilling fluid dispersants which remain operable at temperatures as high as 400° F. and has significantly greater solids tolerance. It provides a drilling fluid with a dispersant which is operable at high temperatures and high solids.

When employing a water-based clay drilling fluid with this dispersant which remains stable at this higher temperature, it is possible to drill into deep formations where temperatures are above 350° F.

By neutralization of a polyacrylic or polymethacrylic acid or copolymers thereof with alkanolamine, alkylamine, mixtures of alkanolamine and alkylamine, mixtures of lithium and alkanolamine, mixtures of lithium and alkylamine or mixtures of lithium, alkanolamine and alkylamine a solids tolerant and high temperature stable dispersant as well as a stable drilling fluid, is obtained.

For example, the polyacrylic acid, polymethacrylic acid or copolymer thereof is neutralized to a pH from about 6 to about 8.5 with one or more alkanolamine having from 2 to 12 carbon atoms such as monoethanolamine, diethanolamine, triethanolamine, propanolamine, isopropanolamine, diisopropanolamine, triisopropanolamine, butanolamine, dimethyl ethanolamine, diethylethanolamine or the like as well as their isomers and homologs and/or one or more alkylamines having from 2 to 12 carbon atoms such as monoethylamine, diethylamine, triethylamine, propylamine, butylamine, hexylamine, dodecylamine as well as their isomers and homologs. Where alkanolamines and/or alkylamines are used with lithium, e.g., as lithium hydroxide, neutralization is accomplished by using the neutralizing agents sequentially or as a mixture. These procedures are well known and need not be described in detail here. Further, where the aforesaid alkanolamine and/or alkylamine are used with, e.g., lithium hydroxide, the polyacrylic acid, polymethacrylic acid or copolymer thereof is likewise neutralized to a pH from about 6 to about 8.5. In such instance, the lithium, e.g., lithium hydroxide, is used to give from about 30% to about 70% of the desired neutralization of the polymer while the alkanolamine and/or the alkylamine is used to give from about 70% to about 30% of the desired neutralization of the polymer.

The salt of polyacrylic acid or polymethacrylic acid or copolymer may be added to the drilling fluid in anhydrous, solution, suspension or emulsion form.

Useful copolymers such as copolymers prepared from acrylic acid or methacrylic acid with comonomers such as maleic anhydride, acrylamide, 2-acrylamido-2-methyl propane sulfonic acid, styrene sulfonic acid and vinyl sulfonic acid or the like, may be used. These copolymers should contain at least 50% by weight of acrylic acid or methacrylic acid. The copolymers are neutralized to a pH of from about 6 to about 8.5 with one of the above basic materials.

PROCEDURE

The terms K and n are used in rheological Power Law Models. These terms are calculated from 600 RPM and 300 RPM Dial Readings taken with the direct indicating viscometer using the following formulas: ##EQU1## The constant K is the value of the shear stress at a shear rate of 1 sec⁻¹. It is measured by extrapolating the straight line of the log of the shear stress versus the log of the shear rate between 10 and 100 sec⁻¹ back to a value of sec⁻¹. The exponent n is determined by measuring the slope of the curve when plotting the log of the shear stress versus the log of the shear rate between 10 and 100 sec⁻¹. The constant K is the consistency index, expressed in lb-sec^(n) /sq. ft. while n is a dimensionless flow behavior index.

The plastic viscosity, PV, is a measure of the internal resistance to fluid flow attributable to the amount, type, and size of solids present in a given fluid. The value, expressed in centipoises, is proportional to the slope of the consistency curve determined in the region of laminar flow for materials obeying Bingham's Law of Plastic Flow. When using the direct indicating viscometer, the plastic viscosity is found by subtracting the 300 rpm reading corresponding to a shear rate of 511 sec⁻¹ from the 600 rpm reading corresponding to a shear rate of 1021 sec⁻¹.

The yield point, YP, also known as the yield value is the resistance to initial flow, or represents the stress required to start fluid movement. This resistance is believed to be due to electrical charges located on or near the surfaces of the particles. Values of yield point and thixotropy, respectively, are measurements of the same fluid properties under dynamic and static states. Bingham yield values reported in lb./100 sq. ft., are determined by using the direct-indicating viscometer and subtracting the plastic viscosity from the 300 rpm reading.

The gel strength is the ability or measure of the ability of a colloid to form gels as a function of time or thixotropy. It is believed to be a measure of the same interparticle forces of a fluid as determined by the yield point except that gel strength is measured under static conditions, yield point under dynamic conditions. The 10 sec. gel strength measurements are initial and the 10 minute are later measurements. The measured initial gel strength of a fluid is the maximum reading (deflection) taken from a direct reading viscometer after the fluid has been static for 10 seconds. This test procedure is described in API RP 13B. The 10 minute gel strength of a fluid is the maximum reading (deflection) taken with a direct reading viscometer after the fluid has been quiescent for 10 minutes. Gel strength is a pressure unit measurement reported in lb./100 sq. ft.

The Fann viscometer (Model 35-A) Meter is a direct reading viscometer, having an outer cylinder which can be rotated at 600, 300, 200, 100, 6 and 3 revolutions per minute (rpm). An inner, concentric cylinder is connected to a scale to permit the operator to read same. The reading at 600 rpm and 300 rpm are recorded. From these readings, plastic viscosity and yield point can be calculated.

The yield point is the parameter of particular interest to this invention. Generally, a lower yield point value indicated that the dispersant is effective in the particular drilling fluid being tested.

EVALUATION OF POLYMERS AS MUD DISPERSANT

The following procedures may be utilized to evaluate salts of polymers as dispersants in fresh water and seawater dispersant mud formulations.

PREPARATION OF TEST SAMPLES

A 350 ml sample of dispersant mud formulation is placed in a stainless steel beaker. With thorough mixing, the polymer is added slowly to the mud and mixed for an additional 15-20 minutes. Mud pH is monitored during mixing and adjusted if necessary. After mixing, viscosities and gel strength of the mud are measured using a Fann viscometer (Model 35-A).

AGING TEST

Equipment: Aging cell, Model #76017 obtained from NL Baroid, Texas. Roller or forced air oven.

Procedure:

(a) Mud containing polymer is placed in aging cell.

(b) The contents of the cell are pressurized with nitrogen gas.

(c) The cell is then placed in a roller over pre-heated to the desired heat aging temperature (dynamic heat aging) or a forced air oven (static heat aging) for 16 hours. All testing is dynamic heat aging unless indicated otherwise.

(d) At the end of the heat aging period, the aging cell is removed from the oven, cooled under cold running water, pressure released and the aged mud transferred into a stainless steel beaker.

(e) Mud pH is checked and if necessary, adjusted to between 9.0 to 10.0 after hot rolling. Rheology measurements are made with Fann viscometer (Model 35-A).

(f) After hot rolling data is gathered, muds are remixed and placed in the cells and statically aged for 16 hours at the desired temperature.

(g) At the end of the heat aging period, the aging cell is removed from the oven, cooled under cold running water, pressure released and the aged mud transferred into a stainless steel beaker.

(h) Rheology and fluid loss measurements are made using API procedure and equipment.

MUD RHEOLOGY

Plastic viscosity (PV), yield point (YP) and gel strengths at 10 second and 10 minute intervals are measured using API procedure RP13B.

MOLECULAR WEIGHTS

Molecular weights of polymers are determined by gel permeation chromatography using polystyrene sulfonic acid as the standard.

For a fuller understanding of the nature and advantages of this invention, reference may be made to the following examples. These examples are given merely to illustrate the invention and are not to be construed in a limiting sense. All quantities, proportions and percentages are by weight and all references to temperature are °F. unless otherwise indicated.

In the examples all references to pounds per barrel of drilling fluid are to a 42 gallon barrel of the drilling fluid and shown as ppb. References to pounds per gallon of drilling fluid are shown as ppg.

EXAMPLE I

This example demonstrates use of mono, di- and tri-alkanolamine salts of polyacrylic acid as dispersants in fresh water drilling fluids. Monoethanolamine, diethanolamine and triethanolamine salts of polyacrylic acid having a weight average molecular weight of about 5,000 were prepared by neutralizing the acid with each amine. Aqueous solutions of these salts were then added as dispersants to Drilling Fluid Samples I and II.

Drilling Fluid Sample I was a 12 ppg (pound per gallon) fresh water mud having the following compositions:

300 g of prehydrated gel slurry (22.5 ppb Wyoming bentonite)

1 g of aqueous solution of dispersant (by activity)

pH 9-10 of 25% by weight NaOH solution

200 g of barite

Drilling Mud Sample I was initial sample and Drilling Mud Sample II contained 30 g of calcium bentonite as solids contamination. Drilling Mud Sample II HR was obtained after Sample II was hot rolled at 150° F. for 16 hours.

Results obtained with these samples are given in Table I.

Laboratory prepared muds of fresh water, 12 ppg and seawater, 12 ppg were prepared and tested initially, after hot rolling at 150° F. for 16 hours and after static aging at 400° F. for 16 hours. Muds with the preferred dispersants were also tested under dynamic temperature and pressure by the use of the Fann viscometer (model 50C).

Compositions of mud formulations are given below:

DISPERSANT MUD FORMULATIONS

Formulations were prepared using the order of addition shown below:

    ______________________________________                                         A.     Fresh Water, 12 ppg Mud                                                 1.     Prehydrated gel slurry                                                                               300    g                                                 (22.5 ppg Wyoming Bentonite)                                            2.     Dispersant            X                                                 3.     NaOH, 25% solution    9-10   pH                                         4.     Barite                200    g                                                 Mix 10 minutes                                                          5.     Calcium bentonite     15     g                                                 (for solids contamination)                                              B.     Seawater, 12 ppg Mud                                                    1.     Prehydrated gel slurry                                                                               300    g                                          2.     Sea salt              14.7   g                                                 Mix 2 minutes                                                           3.     Dispersant            X                                                 4.     NaOH, 25% solution    9-10   pH                                         5.     Barite                200    g                                                 Mix 10 minutes                                                          6.     Calcium bentonite     15     g                                                 (for solids contamination)                                                     Mix 5 minutes                                                           ______________________________________                                    

The following sets forth the abbreviations for the dispersants present in the examples and where appropriate additional information.

MEA-AA: Monoethanolamine salt of polyacrylic acid having a weight average molecular weight of 5,000 and a pH of 7.8 to 8.0.

DEA-AA: Diethanolamine salt of polyacrylic acid having a weight average molecular weight of 5,000 and a pH of 7.8 to 8.0.

TEA-AA: Triethanolamine salt of polyacrylic acid having a weight average molecular weight of 5,000 and a pH of 7.8 to 8.0.

TEA-Li-AA: Mixed lithium and triethanolamine salt of polyacrylic acid having a weight average molecular weight of 5,000 and a pH of 7.8 to 8.0. Neutralization was complete, i.e., 100% contributed as follows: Neutralization by triethanolamine=54%. Neutralization by lithium hydroxide=46%. In this instance, the polymer salt was prepared by partially neutralizing the polyacrylic acid first with triethanolamine to 54% neutralization. Neutralization was then completed by addition of lithium hydroxide.

TIPA-AA: Triisopropanolamine salt of polyacrylic acid having a weight average molecular weight of 5,000 and a pH of 7.8 to 8.0.

Li-AA: Lithium salt of polyacrylic acid having a weight average molecular weight of 5,000 and a pH of 7.8 to 8.5.

AMP-AA: Amino methyl propanolamine salt of polyacrylic acid acid having a weight average molecular weight of 5,000 and a pH of 7.8 to 8.5.

Na-AA: Sodium salt of polyacrylic acid having a weight average molecular weight of 5,000 and a pH of 7.8 to 8.5.

TEA-AA: Triethanolamine salt of polyacrylic acid having a weight average molecular weight of 5,000 and a pH of 4.3 (16% neutralized).

AA-MA: Acrylic acid maleic anhydride copolymer of molecular weight 5000 and pH=7 to 8 (ratios of monomers shown in Table IX).

Na-AMD-AMPS: Sodium salt of acrylamide (80% by wt.), 2-acrylamido-2-methylpropane sulfonic acid (20% by wt.) copolymer of molecular weight=6500 and pH=6.8.

                                      TABLE I                                      __________________________________________________________________________     Alkanolamine Salts of Polyacrylic Acid                                         as Fresh Water Mud Dispersants                                                 Dispersant                                                                     Drilling MEA--AA   DEA--AA  TEA--AA                                            Fluid Sample*                                                                           I II  IIHR                                                                               I II IIHR                                                                               I II IIHR                                          __________________________________________________________________________     Fann 35 viscosity                                                              readings at                                                                    600 rpm  83                                                                               218  300+                                                                              75                                                                               203                                                                               290 60                                                                               127                                                                               190                                           300 rpm  46                                                                               139 220 42                                                                               128                                                                               195 33                                                                               78 120                                           200 rpm  33                                                                               107 175 30                                                                               98 155 24                                                                               57 93                                            100 rpm  19                                                                               66  117 17                                                                               60 102 13                                                                               34 57                                             6 rpm    2                                                                               8   20   1                                                                                7  18  1                                                                                4  7                                             3 rpm    1                                                                               5   12   1                                                                                4  10  1                                                                                3  5                                            Plastic  37                                                                               79  --  33                                                                               75  95 27                                                                               49 70                                            viscosity, cps                                                                 Yield point,                                                                             9                                                                               60  --    9                                                                              53 100  6                                                                               29 50                                            lb/100 sq. ft.                                                                 10 second gel                                                                            2                                                                               5   13   1                                                                                4  11  2                                                                                3  5                                            10 minute gel                                                                            2                                                                               7   15   1                                                                                6  11  1                                                                                3  7                                            __________________________________________________________________________      *pH adjusted to 9.5-10.5.                                                

This table shows the effectiveness of triethanolamine salt over that of di and monoethanolamine salts.

                                      TABLE II                                     __________________________________________________________________________     1 ppb (by activity) Dispersant in 12 ppg Fresh Water Mud                       Containing Calcium Bentonite as Solid Contaminant,                             Initial Test Data, pH Adjusted to about 10.0                                            Fann 35 Viscosity Reading                                                                              Bingham                                                at RPM          Gel Strength                                                                           Plastic                                                                              Power Law                               Dispersant                                                                              600                                                                               300                                                                               200                                                                               100                                                                               6 3 10 Sec                                                                             10 Min                                                                             PV YP n  K                                    __________________________________________________________________________     TEA--AA   76                                                                               42 30 17 2 1 2   2   34  8 0.86                                                                              0.0022                               TEA--Li--AA                                                                              72                                                                               40 27 16 2 1 1   1   32  8 0.85                                                                              0.0022                               Na--AA   108                                                                               59 43 24 2 1 2   2   49 10 0.87                                                                              0.0027                               TIPA--AA  84                                                                               48 35 19 2 1 2   2   36 12 0.81                                                                              0.0033                               Li--AA   119                                                                               68 50 28 2 1 2   2   51 17 0.81                                                                              0.0047                               AMP--AA  113                                                                               67 48 28 3 2 1   2   46 21 0.75                                                                              0.0065                               TEA--AA  128                                                                               77 57 34 5 3 5   7   51 26 0.73                                                                              0.0085                               (16% neutralized)                                                              __________________________________________________________________________

                                      TABLE III                                    __________________________________________________________________________     1 ppb (by activity) Dispersant in 12 ppg Fresh Water Mud                       Containing Calcium Bentonite as Solid Contaminant, Hot                         Rolled at 150° F. for 16 Hours, pH Adjusted to about 10.0                       Fann 35 Viscosity Reading                                                                              Bingham                                                at RPM          Gel Strength                                                                           Plastic                                                                              Power Law                                Dispersant                                                                             600                                                                               300                                                                               200                                                                               100                                                                               6 3 10 Sec                                                                             10 Min                                                                             PV YP n  K                                     __________________________________________________________________________     TEA--Li--AA                                                                            113                                                                                66                                                                               48 27 2 1 2   2   47 19 0.78                                                                              0.0056                                TEA--AA 122                                                                                72                                                                               53 31 4 2 3   3   50 22 0.76                                                                              0.0067                                TIPA--AA                                                                               147                                                                                90                                                                               67 40 5 3 3   3   57 33 0.71                                                                              0.0116                                Na--AA  179                                                                               109                                                                               80 48 6 4 6   6   70 39 0.72                                                                              0.0134                                TEA--AA 181                                                                               115                                                                               87 54 8 6 7   9   66 49 0.65                                                                              0.0208                                partial                                                                        AMP--AA 196                                                                               125                                                                               95 59 9 5 5   6   71 54 0.65                                                                              0.0233                                Li--AA  209                                                                               132                                                                               99 61 8 5 5   6   77 55 0.66                                                                              0.0226                                __________________________________________________________________________

                                      TABLE IV                                     __________________________________________________________________________     1 ppb (by activity) Dispersant in 12 ppg Fresh Water Mud Containing            Calcium Bentonite as Solid Contaminant, Hot Rolled at 150° F. for       16 Hours and Then Static Aged at 400° F. for 16 Hours                            Fann 35 Viscosity Reading Bingham                                              at RPM            Gel Strength                                                                           Plastic      Power Law                      Dispersant                                                                              600                                                                               300                                                                               200                                                                               100                                                                               6  3  10 Sec                                                                             10 Min                                                                             PV YP pH Shear                                                                              n  K                           __________________________________________________________________________     TEA--AA  118                                                                                70                                                                               51 31 3  2  2   2   48 22 9.1                                                                               85  0.75                                                                              0.0068                      Li--TEA--AA                                                                             136                                                                                83                                                                               62 37 4  2  3   3   53 30 9.2                                                                               45  0.71                                                                              0.0104                      TIPA--AA 193                                                                               127                                                                               96 60 8  5  5   5   66 61 9.4                                                                               80  0.60                                                                              0.0314                      Na--AA   *  211                                                                               168                                                                               113                                                                               17 11 12  12  *  *  9.2                                                                               320 ** **                          Li--AA   *  254                                                                               207                                                                               144                                                                               29 19 19  20  *  *  8.5                                                                               140 ** **                          TEA--AA  *  *  *  *  *  *  *   *   *  *  *  *   ** **                          (16% neutralized)                                                              AMP--AA  *  *  *  *  *  *  *   *   *  *  *  *   ** **                          __________________________________________________________________________      * Too thick to measure                                                         ** Too thick to calculate                                                

This series of Tables II-IV dramatically illustrates the superior dispersing effects of the invention. Using YP (yield point) as a guide, in all cases the invention exhibited lower, therefore better dispersing properties. Also the importance of the degree of neutralization is evident by comparing data of the partially neutralized salt (TEA-AA 16% neutralized, pH 4.3) with TEA-AA (8.0 pH). After static aging, the partially neutralized salt was too thick to measure.

                                      TABLE V                                      __________________________________________________________________________     1 ppb (by activity) Dispersant in 12 ppg Sea Water Mud                         Containing Calcium Bentonite as Solid Contaminant,                             Initial Test Data, pH Adjusted to about 10.0 pH                                        Fann 35 Viscosity Reading Bingham                                              at RPM            Gel Strength                                                                           Plastic                                                                              Power Law                              Dispersant                                                                             600                                                                               300                                                                               200                                                                               100                                                                               6  3  10 Sec                                                                             10 Min                                                                             PV YP n  K                                   __________________________________________________________________________     TEA--Li--AA                                                                            35 22 17 12 7  7  11  33  13 9  0.67                                                                              0.0036                              AMP--AA 41 27 22 17 11 11 16  31  14 13 0.60                                                                              0.0067                              Li--AA  40 27 21 16 9  8  14  38  13 14 0.57                                                                              0.0084                              TIPA--AA                                                                               44 30 25 20 14 14 16  19  14 16 0.55                                                                              0.0102                              Na--AA  44 30 24 18 9  9  17  38  14 16 0.55                                                                              0.0102                              TEA--AA 56 41 36 29 19 19 19  24  15 26 0.45                                                                              0.0265                              __________________________________________________________________________

                                      TABLE VI                                     __________________________________________________________________________     1 ppb (by activity) Dispersant in 12 ppg Sea Water Mud                         Containing Calcium Bentonite as Solid Contaminant,                             Hot Rolled at 150° F. for 16 Hours, pH Adjusted to 10.0                         Fann 35 Viscosity Reading                                                                              Bingham                                                at RPM          Gel Strength                                                                           Plastic                                                                              Power Law                                Dispersant                                                                             600                                                                               300                                                                               200                                                                               100                                                                               6 3 10 Sec                                                                             10 Min                                                                             PV YP n  K                                     __________________________________________________________________________     TEA--Li--AA                                                                            46 32 27 20 13                                                                               11                                                                               15  30  14 18 0.52                                                                              0.0131                                TIPA--AA                                                                               51 37 32 26 17                                                                               16                                                                               18  21  14 23 0.46                                                                              0.0220                                Li--AA  53 39 32 25 15                                                                               14                                                                               17  33  14 25 0.44                                                                              0.0264                                Na--AA  63 47 40 33 21                                                                               19                                                                               21  33  16 31 0.42                                                                              0.0359                                AMP--AA 61 47 41 34 23                                                                               22                                                                               24  25  14 33 0.38                                                                              0.0480                                TEA--AA 68 51 44 36 24                                                                               23                                                                               27  17  34 0.41                                                                              0.0409                                   __________________________________________________________________________

                                      TABLE VII                                    __________________________________________________________________________     1 ppb (by activity) Dispersant in 12 ppg Sea Water Mud Containing              Calcium Bentonite as Solid Contaminant, Hot Rolled at 150° C. for       16 Hours and Then Static Aged at 400° F. for 16 Hours                           Fann 35 Viscosity Reading                                                                               Bingham                                               at RPM           Gel Strength                                                                           Plastic      Power Law                        Dispersant                                                                             600                                                                               300                                                                               200                                                                               100                                                                               6  3 10 Sec                                                                             10 Min                                                                             PV YP pH Shear                                                                              n  K                             __________________________________________________________________________     TEA--Li--AA                                                                             84                                                                               75 72 66 54 51                                                                               42  44   9 66 7.6                                                                               45  0.16                                                                              0.2886                        Li--AA  110                                                                               94 87 78 58 57                                                                               46  54  16 78 7.1                                                                               45  0.23                                                                              0.2438                        TEA--AA  97                                                                               89 83 77 61 56                                                                               45  45   8 81 7.7                                                                               70  0.12                                                                              0.4375                        Na--AA  109                                                                               97 91 82 64 61                                                                               50  60  12 85 7.5                                                                               85  0.17                                                                              0.3623                        TIPA--AA                                                                               118                                                                               104                                                                               98 94 77 64                                                                               53  56  14 90 7.7                                                                               120 0.18                                                                              0.3561                        AMP--AA 154                                                                               134                                                                               127                                                                               122                                                                               102                                                                               93                                                                               81  83  20 114                                                                               8.0                                                                               120 0.20                                                                              0.4089                        __________________________________________________________________________

Tables V-VII show data indicating that the mixed lithium-triethanolamine salt (Li-TEA) of acrylic acid is a superior dispersant over other similar polyacrylate dispersants in seawater drilling fluids.

                                      TABLE VIII                                   __________________________________________________________________________     Dynamic Temperature and Pressure Testing of                                    12 ppg Fresh Water Mud Without Calcium Bentonite                                                Using Fann 50-C Setting of 100 RPM 500 psi                               ppb   Viscosity (cps)                                               Dispersant by activity                                                                          100° F.                                                                     150° F.                                                                     200° F.                                                                     250° F.                                                                     300° F.                                                                     350° F.                                                                     400° F.                        __________________________________________________________________________     1 Na--AA--AMD                                                                             1     100 50  25  20  10  110 900                                   2 TEA--AA  1     40  10  10  10  10  10   10                                   3 Li + TEA--AA                                                                            1     40  20  10  10  10  10   45                                   4 Na--AA   1     80  40  20  10  10  40  780                                   __________________________________________________________________________      Table VIII indicates the effectiveness of the invention under dynamic          temperatures and pressure. At 400° F., no viscosity hump was            observed as in the Na--AA or AA--AMD polymers.                           

                                      TABLE IX                                     __________________________________________________________________________     Copolymer Dispersant Data                                                      1 ppb Dispersant (by activity) in 12 ppg Fresh Water                           Mud Containing 15 ppb Calcium Bentonite as a Solid Contaminant                 Dispersant         Fann 35 Viscosity Reading                                   Ratio       Neutralizing                                                                          at RPM                                                      Copolymer                                                                            (% by wt)                                                                            Agent  600                                                                               300                                                                               200                                                                               100                                                                               6 3 10 sec                                                                             10 min                                                                             PV YP                               __________________________________________________________________________     AA--MA                                                                               93-7  TIPA    68                                                                               37 27 15 1 1 1   1   31  6                               AA--MA                                                                                85-15                                                                               TEA     76                                                                               42 31 17 2 1 1   2   34  8                               AA--MA                                                                               93-7  TEA     79                                                                               44 32 18 3 2 2   2   35  9                               AA--MA                                                                               93-7  NaOH    90                                                                               51 37 21 2 1 2   3   39 12                               AA--MA                                                                                85-15                                                                               NaOH   155                                                                               95 71 43 6 4 5   6   60 35                               Hot Rolled at 150° for 16 Hours                                         AA--MA                                                                               93-7  TIPA   108                                                                               62 45 27 3 2 2   3   46 16                               AA--MA                                                                                85-15                                                                               TEA    125                                                                               74 54 32 3 2 3   3   51 23                               AA--MA                                                                               93-7  TEA    130                                                                               77 57 34 4 3 3   3   53 24                               AA--MA                                                                               93-7  NaOH   139                                                                               82 60 35 4 3 4   4   57 25                               AA--MA                                                                                85-15                                                                               NaOH   255                                                                               168                                                                               131                                                                               84 13                                                                               9 9   10  87 81                               __________________________________________________________________________      Table IX illustrates the dispersing effects contributed by alkanolamine        salts of copolymers.                                                     

                                      TABLE X                                      __________________________________________________________________________     Solids Contamination Resistance of 12 ppg Fresh Water                          Mud Containing Indicated Concentration of Dispersant                                                   Gel     Bingham                                                  ppb by        Strength                                                                               Plastic  Power Law                             Dispersant                                                                               Activity                                                                            EX*                                                                               600                                                                               300                                                                               10 Sec                                                                             10 Min                                                                             PV YP pH n  K                                  __________________________________________________________________________     --        0    0   62                                                                               42 12  39  20 22 8.2                                                                               0.56                                                                              0.0135                             --        0    1   72                                                                               49 19  42  23 26 8.1                                                                               0.55                                                                              0.0164                             --        0    2   94                                                                               65 35  36  29 36 7.9                                                                               0.53                                                                              0.0251                             --        0    3  123                                                                               89 47  78  34 55 8.0                                                                               0.47                                                                              0.0517                             --        0    4  151                                                                               104                                                                               63  87  47 57 8.0                                                                               0.54                                                                              0.0388                             --        0    5  196                                                                               139                                                                               79  135 57 82 7.9                                                                               0.50                                                                              0.0674                             TEA--AA   2.50 1   53                                                                               27 3    4  26  1 9.5                                                                               0.97                                                                              0.0007                             TEA--AA   2.50 2   65                                                                               35 3    4  30  5 9.7                                                                               0.89                                                                              0.0014                             TEA--AA   2.50 3   74                                                                               41 3    4  33  8 9.5                                                                               0.85                                                                              0.0022                             TEA--AA   2.50 4   90                                                                               50 3    4  40 10 9.7                                                                               0.85                                                                              0.0027                             TEA--AA   2.50 5  108                                                                               61 4    5  47 14 9.7                                                                               0.82                                                                              0.0038                             TEA--AA   2.50 5H 143                                                                               84 4    5  59 25 9.0                                                                               0.77                                                                              0.0075                             Na--AA    2.50 1   85                                                                               51 8   10  34 17 9.5                                                                               0.74                                                                              0.0055                             Na--AA    2.50 2  118                                                                               73 11  13  45 28 9.7                                                                               0.69                                                                              0.0104                             Na--AA    2.50 3  161                                                                               102                                                                               13  18  59 43 9.6                                                                               0.66                                                                              0.0179                             Na--AA    2.50 4  211                                                                               137                                                                               16  31  74 63 9.6                                                                               0.62                                                                              0.0301                             Na--AA    2.50 5  217                                                                               142                                                                               17  32  75 67 9.9                                                                               0.61                                                                              0.0334                             Na--AA    2.50 5H 297                                                                               201                                                                               23  30  96 105                                                                               9.2                                                                               0.56                                                                              0.0640                             Na--AA    1.00 0   56                                                                               29 1    1  27  2 10.0                                                                              0.95                                                                              0.0008                             TEA--AA   1.00 0   50                                                                               26 1    1  24  2 10.0                                                                              0.94                                                                              0.0008                             Na--AMD--AMPS                                                                            1.00 0   80                                                                               47 4    4  33 14 10.0                                                                              0.77                                                                              0.0042                             TEA--AA   1.00 2.5                                                                                85                                                                               48 2    2  37 11 10.5                                                                              0.82                                                                              0.0030                             Na--AA    1.00 2.5                                                                               105                                                                               60 2    2  45 15 10.8                                                                              0.81                                                                              0.0042                             Na--AMD--AMPS                                                                            1.00 2.5                                                                               150                                                                               95 7   12  55 40 10.3                                                                              0.66                                                                              0.0167                             TEA--AA   1.00 5  141                                                                               84 2    3  57 27 10.0                                                                              0.75                                                                              0.0085                             Na--AA    1.00 5  204                                                                               127                                                                               5    7  77 50 10.5                                                                              0.68                                                                              0.0191                             Na--AMD--AMPS                                                                            1.00 5  270                                                                               83 16  30  87 96 10.0                                                                              0.56                                                                              0.0591                             TEA--AA   1.00 5H 212                                                                               134                                                                               5    7  78 56 9.3                                                                               0.66                                                                              0.0231                             Na--AA    1.00 5H 291                                                                               189                                                                               9   11  102                                                                               87 9.9                                                                               0.62                                                                              0.0416                             Na--AMD--AMPS                                                                            1.00 5H 300                                                                               250                                                                               24  31  50 200                                                                               9.5                                                                               0.26                                                                              0.5173                             __________________________________________________________________________      *REV Dust Contamination for each example:                                      Ex 1 = 10 ppb 2 = 20 ppb 2.5 = 25 ppb 3 = 30 ppb 4 = 40 ppb 5H = 50 ppb        Hot Rolled                                                                     Note:                                                                          Na refers to the sodium salt of the polymer.                             

Table X dramatically illustrates the superior solids contamination resistance of the invention. With increasing amounts of solids contamination (or REV dust) a laboratory prepared drilling fluid showed relatively little adverse rheological behavior (increasing YP) as compared with other polymers.

While the invention has been described with reference to certain specific embodiments thereof it is understood that it is not to be so limited since alterations and changes may be made therein which are within the full intended scope of the appended claims. 

What is claimed is:
 1. An aqueous clay containing drilling fluid having present, in an amount sufficient to disperse the fluid and to provide resistance to high temperatures and solids contamination of the drilling fluid, at least one salt of a polymer of acrylic or methacrylic acid having at least 50% by weight of acrylic or methacrylic acid with mixtures of lithium and alkanolamine, said alkanolamine containing from 2 to 12 carbon atoms, the polymer having a weight average molecular weight of between about 2,000 and about 15,000 and a pH of from about 6 to about 8.5, the amount of lithium being present to give from about 30% to about 70% of the desired neutralization of said polymer and the amount of alkanolamine being present to give from about 70% to about 30% of the desired neutralization of said polymer.
 2. The drilling fluid of claim 1 wherein there is present from about 0.1 pound per barrel to about 5 pounds per barrel of polymer.
 3. The drilling fluid of claim 1 wherein said polymer is polyacrylic acid.
 4. The drilling fluid of claim 1 wherein said alkanolamine is triethanolamine.
 5. In a method of drilling a well into a subterranean formation in which an aqueous clay containing drilling fluid is circulated into the well, the step of circulating said drilling fluid, containing in an amount sufficient to disperse the drilling fluid to provide resistance to high temperatures and solids contamination of the drilling fluid at least one salt of a polymer of acrylic or methacrylic acid having at least 50% by weight of acrylic or methacrylic acid with mixtures of lithium and alkanolamine, said alkanolamine containing from 2 to 12 carbon atoms, the polymer having a weight average molecular weight of between about 2,000 and about 15,000 and a pH of from about 6 to about 8.5, the amount of lithium being present to give from about 30% to about 70% of the desired neutralization of said polymer and the amount of alkanolamine being present to give from about 70% to about 30% of the desired neutralization of said polymer.
 6. The method of claim 5 wherein the salt is present in an amount of from about 0.1 pound per barrel to about 5 pounds per barrel of drilling fluid.
 7. The method of claim 5 wherein the polymer is polyacrylic acid.
 8. The method of claim 5 wherein said alkanolamine is triethanolamine. 